Modern Physics

Answer Me!!! How much energy does a photon have if the light beam has a wavelength of 720 nm?

Thomson Model This is known as the plum pudding model:

Rutherford’s Experiment Gold foil was bombarded with alpha particles (helium nuclei). Most particles went straight through, showing an atom is primarily empty space. Some alpha particles were deflected along a hyperbolic path when they struck the positive nucleus of the gold.

Rutherford’s Model Most of the mass of the atom is in the central nucleus which is positive. Most of the atom is empty space. Electrons go around the nucleus.

Bohr Model

Electron Cloud Model Electrons don’t follow specific paths in energy levels (orbital paths). Instead, energy levels represent locations with high probability of finding an electron.

Energy Levels In order to move to a higher energy level, a specific amount of energy must be absorbed. If an electron moves to a lower energy level that energy will be released as a photon.

Energy Level - Hydrogen Each of the values represents the amount of energy necessary to bind an electron at that energy level. To find the energy in a specific transition, calculate the difference between the two energy levels. E photon = E i -E f

Practice Problem 1 An electron in a hydrogen atom drops from n=3 to n=2 energy level.  What is the energy of the emitted photon in joules?  Calculate the frequency of the emitted radiation.  What color light is this?

Practice Problem 2 If an electron is excited to the n=3 energy state, how many different frequencies of radiation can be emitted as the electron returns to the ground state?

Practice Problem 3 An electron in a mercury atom drops from energy level i to the ground state by emitting a single photon. What is the energy of this photon?

Spectral Lines When an electron absorbs energy from a photon, a dark band (absorption line) can be seen through a spectroscope. When an electron emits energy, a bright colored band (emission line) can be seen through a spectroscope. Each atom has a specific group of spectral lines that can be used to identify its composition.

Answer Me!!! Where does all of our energy come from?

The Atom An atom is the smallest part of an element that has the characteristics of the element. Atoms are composed of Protons Neutrons Electrons

The Nucleus Protons and neutrons are held in the nucleus of an atom. Protons and neutrons are held together in the nucleus by a strong force. The strong force is a short range attractive force between nucleons.

Nuclear Fission

Mass-Energy Equivalence When an atom or particle is decomposed, some of its mass will be converted into energy according to Einstein’s theory: E = mc 2 E is Energy created (in Joules) m is mass lost (in kg) c is the speed of light in a vacuum (in m/s)

All of the Energy in the Universe? The original source of all the universe’s energy is the conversion of mass to energy.

Practice Problem 4 What is the energy equivalent of a mass of kg?

Practice Problem 5 What is the energy equivalent of the rest mass of a proton? How much energy would be created when a proton and an antiproton annihilate each other?

Answer Me!!! What is matter made from?

Standard Sub-Atomic Particles All matter is classified into two categories: hadrons and leptons. Protons and neutrons are hadrons. Electrons, positrons, neutrinos are leptons.

Quarks There are six distinct types of quarks: up, down, charm, strange, top, bottom. Each quark possesses a fractional charge (+2/3 or -1/3 elementary charge) A Proton is made from three quarks: uud A Neutron is made from three quarks: udd

Anti-quarks Six distinct anti-quarks exist and they are related to the six quarks. If a quark (ex. u) has a charge of +2/3, the anti-quark (ex. ū) has a charge of -2/3.

Hadrons Hadrons are matter that is composed of quarks. Hadrons are divided into two groups – baryons and mesons. Protons, Neutrons and Pions are examples of Hadrons.

Baryons Baryons are heavier particles made of three quarks. Protons (uud) and neutrons (udd) are both baryons.

Meson Mesons are lighter than baryons, but heavier than leptons. Mesons are composed of one quark and one anti-quark. Mesons can have a charge of 0e, +1e or -1e. Example Pion

Leptons Leptons are particles that have very little mass. Leptons are bound with the weak nuclear force. Examples of leptons are: electrons, muons and tau particles. Also, each of these has a counterpart neutrino that is a lepton.

Practice Problem 6 Protons and neutrons are examples of?

Practice Problem 7 Which combination of quarks would produce a neutral baryon?  uud  udd  ūdd  ūūd

Practice Problem 8 During beta decay, a neutron decays into a proton by the introduction of an electron antineutrino. During this process, there is a conversion of  An u quark to a d quark  A d quark to a meson  A baryon to another baryon  A lepton to another baryon

Answer Me!!! Which of the following is a stable baryon?  dsc  ssu  ud  tbs